1. Field of the Invention
The present invention relates to instruments and methods for creating an incision in an intraocular tissue, and more particularly to instruments and methods for creating an incision in the anterior capsule of the eye.
2. Description of Related Art
The function of the human eye is to provide vision by allowing an image to be focused on the retina, which then transports the image via the optic nerve to the brain. In order to focus the image on the retina, there are refracting units in the eye: the eye uses the power of the clear cornea (which adds approximately 43 Diopters of plus power to the eye), and the crystalline lens (which adds 15-20 D of power) to focus an image on the retina, in the back of the eye. The quality of the focused image depends on a variety of factors, including the size and shape of the eye as well as the transparency of the cornea and the lens. A healthy human lens is transparent and biconvex, encapsulated by an elastic basement membrane composed of collagen and attached to the ciliary muscles via zonular fibers. Age, disease or trauma can damage the lens, causing the lens to become less transparent. The lens is then called a cataract. A cataract impairs vision by changing the refractive index of the lens, scattering light rays, and reducing the transparency of the lens. This condition is currently treated by surgically removing the cataract and replacing the impaired lens with an artificial intraocular lens (IOL).
Currently, in the United States, most cataractous lenses are removed using a surgical technique called phacoemulsification. During this type of cataract surgery, a viscoelastic substance is injected into the eye through a small corneal incision of approximately 1.5 mm (the side or “paracentesis” port) to maintain the depth of the anterior chamber. A larger (2-3 mm) incision is then made at the limbus of the eye (where the cornea meets the sclera) or on the edge of the cornea itself. A capsulotomy, as described in detail below, is performed to create a circular central opening in the anterior capsule. The thin phacoemulsification cutting tip is then inserted through the limbal incision, through the opening in the anterior capsule, and into the cataract in order to remove the cataract. After the cataract has been removed, an artificial IOL is slipped through the opening in the anterior capsule, and into the remaining capsular bag.
The creation of a circular central opening in the anterior capsule (a capsulotomy) is a necessary step in cataract surgery that serves two purposes: it allows the surgeon access to the lens so that the cataract can be removed, and it also allows the surgeon to place a posterior chamber intraocular lens (PCIOL) into the capsular bag. The capsulotomy is often the most difficult step in cataract surgery for the novice surgeon to master. Even seasoned surgeons sometimes encounter problems with this step.
Currently, the two most popular techniques for anterior capsulotomy are the “can-opener” technique and the capsulorrhexis. In a can-opener capsulotomy, a needle or a cystotome is inserted through the limbal or corneal incision, and small tears are made in the anterior lens capsule in a circular pattern. When a complete circle has been created, the cystotome or needle is removed from the eye and forceps are introduced into the eye. The center of the anterior capsule is then grasped with forceps and torn away along the perforations. Unfortunately, this procedure of opening the capsule with numerous small capsular tears creates small tags which become a focal area of least resistance and can lead to tears which extend radially and posteriorly to the posterior capsule. Radial tears in the capsule can result in complications, as described above.
The capsulorrhexis is the more commonly used method for the creation of the circular central opening in the anterior capsule. In a capsulorrhexis procedure, a cystotome is inserted into the eye and used to create the initial tear in the anterior capsule. This first tear is made near the center of the eye to increase the distance of the initial flap from the lens equator. In the next step of the capsulorrhexis procedure, either the cystotome or a forceps is used to delicately manipulate the free flap in a circular motion to peel a continuous circular tear in the anterior capsule. This procedure is difficult to control by the surgeon. It is often difficult to visualize the thin capsule (the capsule varies from 2-28 micrometers in thickness, and is thinnest at its anterior and posterior poles). The edge of the capsulorrhexis is particularly difficult to visualize in a dense subcapsular cataract where the red reflex may be absent. In these cases, the surgeon may feel the need to inject a dye such as 10% sodium fluorescein into the eye to stain the capsule and enhance the view of the rhexis. In addition, the tearing motion can lead to a radial tear (an undesirable tear toward the equator and the posterior capsule). Finally, the opening size and position is very hard to control. A capsulotomy that is too small can make the remainder of the surgery very difficult to perform. In addition, small capsular openings tend to seal and form fibrous proliferation, thereby causing glare for the patients post-operatively. Due to the above factors, the capsulorrhexis is widely considered to be one of the most difficult steps in cataract surgery.
If a radial tear occurs during the creation of a capsulotomy, the tear may extend to the posterior capsule, and increase the risk of complications. These complications can include loss of integrity of the capsule, requiring the implantation of a lens other than the preferred PCIOL. Another complication due to a radial tear is vitreous entry into the anterior chamber. In addition, a posterior capsule tear could allow entry of the entire cataract or of pieces of the lens into the posterior chamber, requiring a vitrectomy, and placing the patient at an increased risk of damage to the retina. A capsulotomy that results in a tear of the capsule increases operative time and patient discomfort. It also increases the likelihood of a bad visual outcome for the patient.
The following patents, each of which is incorporated by reference herein in its entirety, are found to be related to the field of surgical apparatus used in the capsulotomy step of cataract surgery:
1. U.S. Pat. No. 5,728,117 issued to Lash on Mar. 17, 1998 for “Retractable Capsulorrehexis Instrument”.
2. U.S. Pat. No. 6,629,980 issued to Eibschitz-Tsimhoni on Oct. 7, 2003 for “Instrument And Method For Creating An Intraocular Incision”.
3. U.S. Pat. No. 6,551,326 issued to Van Heugten, et al. on Apr. 22, 2003 for “Capsulorrhexis Device”.
4. U.S. Pat. No. 7,011,666 issued to Feinsod on Mar. 14, 2006 for “Incising Apparatus For Use In Cataract Surgery”.
5. U.S. Pat. No. 4,766,897 issued to Smirmaul on Aug. 30, 1988 for “Capsulectomy Surgical Instrument”.
6. U.S. Pat. No. 5,135,530 issued to Lehmer on Aug. 4, 1992 for “Anterior Capsular Punch With Deformable Cutting Member.”
7. U.S. Pat. No. 7,763,032 issued to Ellis on Jul. 27, 2010 for “Method and apparatus for forming an aperture in a lens capsule of an eye.”
8. U.S. Pat. No. 5,792,166 issued to Gordon on Aug. 11, 1998 for “Anterior capsulotomy device and procedure.”
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for devices and methods that allow for improved capsulotomy. There also remains a need in the art for such devices and methods that are easy to make and use. The present invention provides a solution for these problems.